Comparison between stellarator and tokamak divertor transport

Feng, Y.; Kobayashi, M.; Lunt, T.; Reiter, D.

doi:10.1088/0741-3335/53/2/024009

Cited by 87 publications

(131 citation statements)

References 52 publications

(90 reference statements)

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“…The differences between tokamak and stellarator divertor physics have recently been reviewed by Feng et al [74], and will therefore only be outlined briefly here. Only two stellarators, W7-AS and LHD, have operated with proper divertors, and these are geometrically very different from each other.…”

Section: Edge and Divertor Physicsmentioning

confidence: 99%

Stellarator and tokamak plasmas: a comparison

Helander

Beidler

Bird

et al. 2012

Plasma Phys. Control. Fusion

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An overview is given of physics differences between stellarators and tokamaks, including magnetohydrodynamic equilibrium, stability, fast-ion physics, plasma rotation, neoclassical and turbulent transport, and edge physics. Regarding microinstabilities, it is shown that the ordinary, collisionless trapped-electron mode is stable in large parts of parameter space in stellarators that have been designed so that the parallel adiabatic invariant decreases with radius. Also, the first global, electromagnetic, gyrokinetic stability calculations done for Wendelstein 7-X suggest that kinetic ballooning modes are more stable than in a typical tokamak.

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Section: Edge and Divertor Physicsmentioning

confidence: 99%

Stellarator and tokamak plasmas: a comparison

Helander

Beidler

Bird

et al. 2012

Plasma Phys. Control. Fusion

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135

181

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“…The poloidal divertor has well-documented advantages and disadvantages over a limited configuration [36]. This concept has a natural analogue in a 3D system in the island divertor [37], where the edge transform 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 is configured to provide a resonant value at the plasma edge, and the resulting island chain is intersected by PFCs. Optimized stellarators also tend to exhibit natural striated patterns of flux mapped from the last closed flux surface (LCFS) to an enclosing shape, exhibiting characteristics determined by the shape of the LCFS [38,39].…”

Section: Divertor Designmentioning

confidence: 99%

Recent advances in stellarator optimization

et al. 2017

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Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed.The purpose of this paper is to outline a select set of new concepts for stellarator optimization that, when taken as a group, present a significant step forward in the stellarator concept.One of the criticisms that has been leveled at existing methods of design is the complexity of the resultant field coils. Recently, a new coil optimization code -COILOPT++, which uses a spline instead of a Fourier representation of the coils, -was written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. The code has been tested by generating coil designs for optimized quasi-axisymmetric stellarator plasma configurations of different aspect ratios. As an initial exercise, a constraint that the windings be vertical 1 was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented.New ideas on methods for the optimization of turbulent transport have garnered much attention since these methods have led to design concepts that are calculated to have reduced turbulent heat loss. We have explored possibilities for generating an experimental database to test whether the reduction in transport that is predicted is consistent with experimental observations. To this end, a series of equilibria that can be made in the now latent QUASAR experiment have been identified that will test the predicted transport scalings. Fast particle confinement studies aimed at developing a generalized optimization algorithm are also discussed. A new algorithm developed for the design of the scraper element on W7-X is presented along with ideas for automating the optimization approach.

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“…The rotational transform of the magnetic field is provided entirely by the currents flowing in external coils and its profile may be chosen to avoid low-order resonances and their accompanying islands in the confinement volume and instead to place such islands at the plasma boundary where their x-points provide a naturally occurring 'island divertor' [7]. However, the classical stellarator needs physics optimization [1,3,4] to allow for integrated discharge scenarios with reactor-relevant plasma parameters.…”

Section: Physics Programmentioning

confidence: 99%

“…One is the combined effect of neoclassical and turbulent transport, another example is the much richer spectrum of unstable Alfvén eigenmodes driven by fast particles [15], the third one is the physics of the island divertor Figure 5: Sequence of investigations to be performed during the second operation phase of Wendelstein 7-X. [7]. A direct extrapolation of Wendelstein 7-X to a stellarator fusion power plant (FPP) would therefore not be without risk of failure, although the degree of risk would certainly be reduced by significant progress in the theoretical models used to explain (and subsequently predict) Wendelstein 7-X and ITER results.…”

Section: Stellarator Reactormentioning

confidence: 99%

Towards assembly completion and preparation of experimental campaigns of Wendelstein 7-X in the perspective of a path to a stellarator fusion power plant

Klinger

Baylard

Beidler

et al. 2013

Fusion Engineering and Design

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The superconducting stellarator device Wendelstein 7-X, currently under construction, is the key device for the proof of stellarator optimization principles. To establish the optimized stellarator as a serious candidate for a fusion reactor, reactor-relevant dimensionless plasma parameters must be achieved in fully integrated steady-state scenarios. After more than 10 years of construction time, the completion of the device is now approaching rapidly (mid 2014). We discuss the most important lessons learned during the device assembly and first experiences with coming major work packages. Those are (a) assembly of about 2500 large, water-cooled, 3d-shaped in-vessel component elements; (b) assembly of in total 14 superconducting current leads, one pair for each coil type, (c) assembly of the device periphery including diagnostics and heating systems. In the second part we report on the present status of planning for the first operation phase (5 − 10 s discharge duration at 8 MW heating power), the completion and hardening of the device for full power steady-state operation, and the second operation phase (up to 30 min discharge duration at 10 MW heating power). It is the ultimate goal of operation phase one to develop credible and robust discharge scenarios for the high-power steady-state operation phase two. Beyond the improved equilibrium, confinement, and stability properties owing to stellarator optimization, this requires density control, impurity control, edge iota control as well as high density microwave heating. Of paramount importance is the operation of the island divertor, which is realized in the first operation phase as an inertially cooled conventional graphite target divertor. It will be replaced later on by the steady-state capable island divertor with its water-cooled carbon fiber reinforced carbon target elements.

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Comparison between stellarator and tokamak divertor transport

Abstract: The

Cited by 87 publications

References 52 publications

Stellarator and tokamak plasmas: a comparison

Stellarator and tokamak plasmas: a comparison

Recent advances in stellarator optimization

Towards assembly completion and preparation of experimental campaigns of Wendelstein 7-X in the perspective of a path to a stellarator fusion power plant

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